Threats / SolarWinds / CVE-2021-35247
CVE-2021-35247
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
SolarWinds Serv-U vulnerability
SolarWinds Serv-U versions 15.2.5 and earlier contain improper input validation allowing attackers to send unsanitized queries, enabling unauthorized access and data manipulation.
Verdict
Today item — known-exploited.
This improper input validation vulnerability in Serv-U has been exploited in the wild. Attackers can bypass security controls by crafting malicious queries, potentially leading to unauthorized system access, data exfiltration, or lateral movement within affected environments.
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
3 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-01-21).
Probability (EPSS)
EPSS 0.03359 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: SolarWinds, Serv-U. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-20 Improper Input Validation.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft and send queries without proper sanitization to bypass input validation controls.
Business
Attackers gain unauthorized access to file transfer systems and sensitive data stored within Serv-U instances.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I execute commands or access resources through the unvalidated query interface to establish persistence.
Business
Compromised Serv-U servers become pivot points for lateral movement and extended network compromise.
3
Lateral reach — past segmentation narrative 3
Attacker
I extract credentials, configuration data, or customer files accessible through the vulnerable query mechanism.
Business
Data breach exposes confidential information, triggering regulatory penalties, customer notification costs, and reputational damage.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05
Coverage & confidence
— what we know, and what we don’tEstablished (cited)
Coverage gaps — stated, not hidden
Disclosure & credit2
Catalogued by SolarWindsCNA
Credited with finding itSolarWinds would like to thank Jonathan Bar Or of Microsoft (@yo_yo_yo_jbo) for reporting this vulnerabilityunspecified